1. Field of the Invention
The present invention relates to an improved process for the oxidation of n-butane to maleic anhydride. The specific improvement of the present invention resides in the use of a series of reactors to accomplish the n-butane oxidation with removal of product maleic anhydride from the effluent of a reactor prior to forwarding the remaining gases together with supplemental n-butane to the next in the series of oxidation reactors. Air or oxygen enriched air can be used to accomplish the oxidation.
2. Description of the Prior Art
The production of maleic anhydride by the oxidation of n-butane is, of course, by now a well known and commercially practiced process. Primarily the maleic anhydride is produced by introducing n-butane in admixture with air into contact with an oxidation catalyst such as a VPO catalyst under conditions such that the n-butane is oxidized to maleic anhydride. In conventional practices, the effluent from this reactor may be cooled to partially condense the product maleic anhydride from the effluent gases. The gaseous product, with or without partial maleic anhydride removal, is scrubbed using a solvent, usually water, to recover all of product maleic anhydride. The remaining gases, containing unconverted n-butane, are commonly incinerated in an effluent gas incinerator prior to venting to atmosphere.
There are references which relate to the use of more than one reactor in series in order to produce maleic anhydride. Specifically, U.S. Pat. No. 5,360,916 provides a two stage process for maleic anhydride production wherein n-butane is oxidized in a first reaction zone and the effluent from this zone is passed together with supplemental n-butane to a second reactor in series in order to complete production of the maleic anhydride. A feature of the process described in this patent is that there is at most only a partial removal of maleic anhydride by condensation from the effluent from the first of the reactors prior to introduction into the second and last in the series of reactors.
A literature article by Bissot et al. entitled "Oxidation of Butane to Malic Anhydride" appearing in IEC vol. 2 No. 1 March 1963, pages 57-60 discloses a process for maleic anhydride production wherein n-butane is oxidized in a series of fluidized bed reactors using a cobalt or nickel molybdate catalyst, the effluent from the first of the reactors passing to the second reactor after intermediate removal of product maleic anhydride. There is no teaching in this literature reference of the addition of supplemental n-butane to the effluent of the first of the reactors prior to continuing the reaction in a second reactor after maleic anhydride removal.